You may want to consider using an SAE Connectoer (radio shack), the cig lighter will require a 3" deep hole and finishing work, the SAE is a simple wire that you can tap onto the DC and then rewire the Fan cord with the mate SAE connector, and Velcro or surface mount the plug.
Just an option as long as you are picking up DC 12 volt for the Fans. There are finished looking ones as well i picked this picture since it show the separate wires
2011 GMC 3500HD 4x4 Crew DRW Duramax
2012 Sierra 365SAQ
2006 Police Roadking FLHPi